WORKSHOP ON GEOTHERMAL RESERVOIR ENGINEERING* Paul Kruger and Henry J. Ramey, Jr. Stan ford Geo the rma 1 Program Stanford University Stanford, California Workshop Report December 1 5- 1 7, 1975 J; Conducted under Grant No. NSF-AER-72-03490 sponsored by the RANN program of the National Science Foundation. TABLE OF CONTENTS Page Summary of the Workshop - P. Kruger .................. 1 Rapporteur Reports Reservoir Physics - P. A. Witherspoon ............... 4 Well Testing - H. J. Ramey, Jr. ................ 6 Field Development - G. Frye .................... 8 Well Stimulation - M. Nathenson .................. 9 Model ing - J. W. Mercer .................. 12 Overv iews A Programmatic View of Geothermal Reservoir Engineering - R. Coryell 16 The Birth of Geothermal Reservoir Engineering - H. J. Ramey, Jr. .. 20 Reservoir Phvsics Summary Description of Research Activities - D. R. Kassoy ...... 23 Heat and Fluid Flow Experiments to Measure Geothermal Reservoir Physical Parameters - W. E. Brigham ............... 26 An Attempt to Correlate Kh Distribution with Geological Structure of Larderello Geothermal Field - R. Celati, G. Neri, F. Perusini, and P. Squarci ......................... 37 Fluid Flow in Geothermal Reservoirs - J. C. Martin ......... 42 Fracture Flow in Geothermal Reservoirs - G. Bodvarsson ....... 45 Reservoir Factors Determining the Fraction of Stored Energy Recoverable from Hydrothermal Convection Systems - M. Nathenson . 50 Utilization of Gravimetric Data for Estimation of Hydrothermal Reservoir Characteristics in the East Mesa Field, Imperial Valley, California - T, Meidav, R. James, and S. Sanyal ........ 52 An Investigation of Screening Geothermal Production We1 1s from Effects of Reinjection - C. F. Tsang and P. A. Witherspoon ... 62 Land Surface Subsidence Associated with Geothermal Energy Production - S. K. Garg ..................... 65 Well Testing Pressure and Temperature Buildup in Geothermal Wells - M. S. Gulati . 69 Well Log Analysis and Well Testing in the Heber Geothermal Field - L. Mann ................... 74 I Geothermal Well Testing at Roosevelt KGRA, Beaver County, Utah - D. C.Harban . 77 Shell's Activity in The Geysers Area - E. L. Fehlberg . 84 Water Entry Below Steam Production: A Case History at The Geysers - G. Frye . , . 89 An Interference Test in Alfina Geothermal Field (Northern Latium, Italy) - A. Barelli and G. Manetti . 93 Horner Method Applied to Build-Up Tests on Travale 22 Well - A. Barelli, R. Celati, G. Manetti, and G. Neri . 101 Study of a Geothermal Field in the Asal Active Volcanic Rift Zone (French Territory of Afars and Issas, East Africa) - A. C. Gringarten and L. Stieltjes . 113 Raft River Geothermal Reservoir Engineering and Well Stimulation - J. F. Kunze, L. G. Miller, and R. C. Stoker . 117 Initial Results of Reservoir Production Tests, Raft River Geothermal Project, Idaho - T. N. Narasimhan and P. A. Witherspoon . 124 Field Development An Approach to Geothermal Development - R. A. Wooding . 126 Geopressured Geothermal Reservoir Engineering Research at the University of Texas - R. M. Knapp, M. H. Dorfman, 0. F. Isokrari 130 SDGEE Pioneering Geothermal Test Work in the Imperial Valley of Southern California - G. L. Lombard and J. M. Nugent . 135 Niland Reservoir Monitoring and Evaluation Operating Program - T. C. Hinrichs . 143 East Mesa Reservoir - T. L. Gould . 146 The PG&E Geysers Power Plant - A Utility Company's Viewpoint - L. J. Woitke . I , . 153 Geothermal Reservoir Pressure Requirements for Production - J. T. Kuwada . 156 On the Optimal Rate of Geothermal Energy Extraction - C. R. Scherer . 161 Economic Modeling for Geothermal Reservoirs and Power Plants - C. H. Bloomster . 167 We1 1 Stimulation Physical Models of Stimulated Geothermal Reservoirs - P. Kruger . I69 Hydraul ic-Fracture Geothermal Reservoir Engineering - H. D. Murphy . 174 Model Experiments in Hydraulic Fracture - J. Dundurs . 178 Analytical Study of Crack Growth and Shape by Hydraulic Fracturing of Rocks - T. Mura, L. M. Keer, and H. Ab6 . 180 Control of Silica Scaling - H. L. Barnes and J. D. Rimstidt . 185 Predicting Explosion-Generated Permeability around Geothermal Wells - C. R. McKee and M. E. Hanson . 192 ii Model ing Summary of our Research in Geothermal Reservoir Simulation - C. R. Faust and J. W. Mercer - ................. 198 The Princeton Geothermal Research Program - George Pinder ...... 199 Numerical Calculation of Multiphase Fluid and Heat Flow in Hydrothermal Reservoirs - J. W. Pritchett ............ 201 Methods of Solution of the Equations for Convection in Porous Media, with Geothermal Applications - R. A. Wooding ....... 2 06 A Hele-Shaw Model of Heat Convection in Porous Media under Geothermal Conditions - H. W. Shen ............... 213 Numerical and Analytical Studies on Heat and Mass Transfer in Volcanic Island Geothermal Reservoirs - Ping Cheng ....... 219 Research on Numerical Modeling of Liquid Geothermal Systems - blichael Sorey .......................... 225 Finite Element Solution of Geothermal Energy Extraction - Z. P. Ba?ant, S. Nemat-Nasser, and H. Ohtsubo .......... 232 Numerical Model ing of Hydrothermal Reactions in Geothermal Reservoirs - C. G. Sammis .................... 240 Progress Report on a Mathematical Model of a Parallelepiped Reservoir with No Penetrating Wellbore and Mixed Boundary Conditions - A. Barelli, G. Manetti, R. Celati, and G. Neri ......... 242 Fundamental Study of Changing of Phase in Porous Materials - Serge Bories .......................... 247 Thermal Depletion of Liquid-Dominated Geothermal Reservoirs with Fracture and Pore Permeability - P. W. Kasameyer and R. C. Schroeder ......................... 249 Geothermal Energy from a Borehole in Hot Dry Rock - A Preliminary Study - D. Sharma and T. Maini .. , .............. 2 58 The Use of General Sensitivity Theory to Analyze the Geothermal Reservoir Model's Sensitivity to the Permeability Functions - R. W. Atherton ......................... 2 67 iii 1 NTRODUCT ION Although geothermal energy was first converted to electricity more than 70 years ago, until recently little public demand for its widespread use existed. Geothermal energy has been considered an attractive alternate source of energy for more than a decade in many developed as well as un- developed countries and the international awareness of the growing deficit of fossil fuels has sparked accelerated interest in determining national resources and utilization technologies. As of 1976, the total world generating capacity for generating electricity from geothermal resources is about 1100 MW (equal to that of one modern nuclear power plant) and more than 3/4 of it is produced at only two sites, The Geysers in California and the Tuscany fields in Italy. Many problems have been identified which beset the rapid development of geothermal resources, covering the entire "fuel cycle" from exploration through conversion and residuals control. The major problem is the in- flexity of natural geothermal resources which occur in a wide variety of hydrogeologic, thermal, and chemical qualities. Utilization must be designed to fit the specific characteristics of individual resources. Since the thermal efficiencies for conversion to electric energy are very low even for the two known highest quality hydrothermal resources, in- dustrial development awaits greater economies in resource exploration and evaluation, energy extraction, and utilization technologies. To compound the problems, development is occurring in an era of increased public aware- ness about institutional and environmental concerns. As a result, a formidable array of legal, social, and regulatory problems also requires resolution. As the developnent of a geothermal industry proceeds, these many problems are being evaluated generally by the sector of the national economy that has had experience in solving similar problems for other resources. The exploration for geothermal resources has been undertaken largely by the energy resource companies that use subsurface geosciences and the drill rig as their mode of operation. Conversion to electricity, presently the major utilization of geothermal resources, has been under- taken by the private and public utility industry. And the institutional problems are within the domain of the several levels of public administration ranging from the Federal government to county and township agencies. It can be assumed that as the public demand for energy to be supplied by geothermal resources increases, accommodations between suppliers, regulators, and the public will be achieved. It can also be assumed that adequate technology will be developed to utilize "commercial" resources for both electrical and direct thermal applications. Thus, the major area for concern in the accelerated development of a geothermal industry is the definition of what constitutes a "commercial" resource. From a pragmatic point of view, a "commercial" resource is one from which a sufficient amount of geothermal resource can be extracted to sell to a willing buyer at a profitable price over some reasonable period of time. Exploration for geothermal resources, in spite of the aforementioned institutional difficulties, is underway. Recent estimates by the U. S. -1- Geological Survey indicate a large number of potential areas of geothermal resources in the U. S. alone. The assessment of "commercial" viability of these resources is the difficult task, due in part to the small number of existing operational fields, and also in part to the empirical history of geothermal power plant development,